STABLE-15: ZFS incorrectly orders metaslabs (?)

Hello.

So I like, thought about looking at 15 on my book. As I'm normally using 
STABLE on my workplace and non-prod servers this wasn't that much scary, 
so I just went ahead and compiled kernel. Everything seems to be working 
pretty much fine, so I also updated world and kernel modules (so I can 
use desktop). Again, everything was working pretty much fine, so I went 
ahead rebuilding packages. And after a few dozen my host just stuck. I 
rebooted only to face instapanic on boot, someting like this:

https://t.me/freebsd_ua/18931

I tried booting from old kernel (STABLE-14), and suddenly host just 
booted. Then I tried repating steps under 15 to make sure it's real bug. 
And after some disk activity host stuck again. This time, however, 14 
wasn't able to boot too:

https://t.me/freebsd_ua/18948

My setup:

* Custom kernel, mostly based off MINIMAL.
* ZFS was NOT upgraded.
* There was a number of features enabled on ZFS, like checksums, big 
blocks, dedup, etc.

I'll try to boot GENERIC 15 on the pool to check.

Hope that helps someone to debug the issue. Thanks.

-- 
Sphinx of black quartz judge my vow.